BrightSource Energy said Monday that it has struck a deal to add energy storage systems to three massive solar thermal power plants it will build to supply electricity to utility Southern California Edison.

Energy storage will allow the plants to operate into the night, meaning that BrightSource can now forgo building one 200-megawatt solar station that previously was needed to meet its obligation to generate 4 million megawatt-hours of electricity annually for the utility.

“It’s a huge advantage,” John Woolard, BrightSource’s chief executive, said in an interview Monday. “We came out very strongly with what I believe is the largest solar storage deal in the world.”

BrightSource spokesman Keely Wachs said in an e-mail that only six of the seven planned solar “power tower” stations will need to be built, saving some 1,280 acres of desert land. If approved by state regulators, the amended contracts with Southern California Edison will also result in lower costs for utility customers, the company said.

Both issues have come to the forefront as some environmentalists increasingly object to industrializing swaths of California’s Mojave Desert for solar power plants. Solar thermal developers, meanwhile, compete against ever-cheaper photovoltaic power plants as the price of solar modules continues to fall.

When four of the nine big solar thermal power plants approved by the California Energy Commission last year changed ownership, the new developers announced they would switch to solar panels like those found on residential rooftops and which convert sunlight directly into electricity.